With the explosive proliferation of color images, there has been growing demand for higher image quality in recent years. In full-color digital copiers or printers, color image data is color-separated through respective color filters of blue, green, and red, and a latent image corresponding to the original image is then developed using respective color developers of yellow, magenta, cyan, and black. In this regard, the coloring power of a colorant in each color developer largely influences image quality. For the dispersion of pigments in various media, however, it is generally difficult to render pigment particles sufficiently fine or to disperse the pigments uniformly.
Typical examples of the yellow colorant include pigments having an isoindoline skeleton, such as C.I. Pigment yellow 185, which has high transparency and coloring power and excellent weather resistance.
This C.I. Pigment yellow 185 tends to self-aggregate due to its pigment character and is known to be dispersed neither sufficiently nor stably as a colorant in a binder resin. Unfortunately, this pigment, albeit excellent in weather resistance, cannot sufficiently exert its original performance in transparency or color saturation. In order to solve such a problem, for example, PTL 1 discloses a pigment dispersant such as a pigment dispersion containing an isoindoline pigment with an introduced sulfonic acid group.
Also, PTL 2 discloses a color filter having a contrast ratio or Y value improved by using Solvent yellow 162 as a phthalocyanine pigment.
The reproducibility of color spaces including Japan Color for printing industry and Adobe RGB for desktop publishing (DTP) has become increasingly important in recent years. For this reproducibility of color spaces, only improvement in the dispersibility of pigments is not sufficient, and it is necessary to use dyes having a wide color gamut. The dyes, however, are known to have weaker light resistance than that of pigments. No dye has been found to be able to resist, at the same level as in pigments, deterioration with age.